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Allogeneic stem cell transplantation (allo-SCT) can be a curative treatment for patients with a hematologic malignancy due to alloreactive T cell responses recognizing minor histocompatibility antigens (MiHA). Yet tumor immune escape mechanisms can cause failure of T cell immunity, leading to relapse. Tumor cells display low expression of costimulatory molecules and can up-regulate coinhibitory molecules that inhibit T cell functionality on ligation with their counter-receptors on the tumor-reactive T cells. The aim of this explorative study was to evaluate immune checkpoint expression profiles on T cell subsets and on cytomegalovirus (CMV)- and/or MiHA-reactive CD8+ T cells of allo-SCT recipients using a 13-color flow cytometry panel, and to correlate these expression patterns to clinical outcomes. MiHA-reactive CD8+ T cells exhibited an early differentiated CD27++/CD28++ phenotype with low KLRG-1 and CD57 expression. These T cells also displayed increased expression of PD-1, TIM-3, and TIGIT compared with total effector memory T cells and CMV-specific CD8+ T cells in healthy donors and allo-SCT recipients. Remarkably, high coexpression of PD-1, TIGIT, and KLRG-1 on MiHA-reactive CD8+ T cells was associated with relapse after allo-SCT. Taken together, these findings indicate that MiHA-specific CD8+ T cells of relapsed patients have a distinctive coinhibitory expression signature compared with patients who stay in remission. This phenotype may serve as a potential monitoring tool in patients. Moreover, these findings suggest that PD-1 and TIGIT play important roles in regulating T cell-mediated tumor control, providing a rationale for immunotherapy with blocking antibodies to treat relapse after allo-SCT.

Contains fulltext : 172057.pdf (Publisher’s version ) (Closed access) Potent immunotherapies are urgently needed to boost antitumor immunity and control disease in cancer patients. As dendritic cells (DCs) are the most powerful APCs, they are an attractive means to reinvigorate T cell responses. An appealing strategy to use the effective Ag processing and presentation machinery, T cell stimulation and cross-talk capacity of natural DC subsets is in vivo tumor Ag delivery. In this context, endocytic C-type lectin receptors are attractive targeting molecules. In this study, we investigated whether CLEC12A efficiently delivers tumor Ags into human DC subsets, facilitating effective induction of CD4(+) and CD8(+) T cell responses. We confirmed that CLEC12A is selectively expressed by myeloid cells, including the myeloid DC subset (mDCs) and the plasmacytoid DC subset (pDCs). Moreover, we demonstrated that these DC subsets efficiently internalize CLEC12A, whereupon it quickly translocates to the early endosomes and subsequently routes to the lysosomes. Notably, CLEC12A Ab targeting did not negatively affect DC maturation or function. Furthermore, CLEC12A-mediated delivery of keyhole limpet hemocyanin resulted in enhanced proliferation and cytokine secretion by keyhole limpet hemocyanin-experienced CD4(+) T cells. Most importantly, CLEC12A-targeted delivery of HA-1 long peptide resulted in efficient Ag cross-presentation by mDCs and pDCs, leading to strong ex vivo activation of HA-1-specific CD8(+) T cells of patients after allogeneic stem cell transplantation. Collectively, these data indicate that CLEC12A is an effective new candidate with great potential for in vivo Ag delivery into mDCs and pDCs, thereby using the specialized functions and cross-talk capacity of these DC subsets to boost tumor-reactive T cell immunity in cancer patients.

Contains fulltext : 190712.pdf (Publisher’s version ) (Closed access) New immunotherapeutic interventions have revolutionized cancer treatment. The immune responsiveness of acute myeloid leukaemia (AML) was first demonstrated by allogeneic stem cell transplantation. In addition, milder immunotherapeutic approaches are exploited. However, the long-term efficacy of these therapies is hampered by various immune resistance and editing mechanisms. In this regard, co-inhibitory signalling pathways have been shown to play a crucial role. Via up-regulation of inhibitory checkpoints, tumour-reactive T cell and Natural Killer cell responses can be strongly impeded. Accordingly, the introduction of checkpoint inhibitors targeting CTLA-4 (CTLA4) and PD-1 (PDCD1, CD279)/PD-L1 (CD274, PDCD1LG1) accomplished a breakthrough in cancer treatment, with impressive clinical responses. Numerous new co-inhibitory players and novel combination therapies are currently investigated for their potential to boost anti-tumour immunity and improve survival of cancer patients. Although the challenge here remains to avoid severe systemic toxicity. This review addresses the involvement of co-inhibitory signalling in AML immune evasion and discusses the opportunities for checkpoint blockers in AML treatment.

Allogeneic stem cell transplantation (allo-SCT) can be a curative treatment for patients with a hematologic malignancy due to alloreactive T cell responses recognizing minor histocompatibility antigens (MiHA). Yet tumor immune escape mechanisms can cause failure of T cell immunity, leading to relapse. Tumor cells display low expression of costimulatory molecules and can up-regulate coinhibitory molecules that inhibit T cell functionality on ligation with their counter-receptors on the tumor-reactive T cells. The aim of this explorative study was to evaluate immune checkpoint expression profiles on T cell subsets and on cytomegalovirus (CMV)- and/or MiHA-reactive CD8

Contains fulltext : 136942.pdf (Publisher’s version ) (Closed access) The superiority of dendritic cells (DCs) as antigen-presenting cells has been exploited in numerous clinical trials, where generally monocyte-derived DCs (Mo-DCs) are injected to induce immunity in patients with cancer or infectious diseases. Despite promising expansion of antigen-specific T cells, the clinical responses following vaccination have been limited, indicating that further improvements of DC vaccine potency are necessary. Pre-clinical studies suggest that vaccination with combination of primary DC subsets, such as myeloid and plasmacytoid blood DCs (mDCs and pDCs, respectively), may result in stronger clinical responses. However, it is a challenge to obtain high enough numbers of primary DCs for immunotherapy, since their frequency in blood is very low. We therefore explored the possibility to generate them from hematopoietic progenitor cells (HPCs). Here, we show that by inhibiting the aryl hydrocarbon receptor with its antagonist StemRegenin 1 (SR1), clinical-scale numbers of functional BDCA2+BDCA4+ pDCs, BDCA1+ mDCs, and BDCA3+DNGR1+ mDCs can be efficiently generated from human CD34+ HPCs. The ex vivo-generated DCs were phenotypically and functionally comparable to peripheral blood DCs. They secreted high levels of pro-inflammatory cytokines such as interferon (IFN)-alpha, interleukin (IL)-12, and tumor necrosis factor (TNF)-alpha and upregulated co-stimulatory molecules and maturation markers following stimulation with Toll-like receptor (TLR) ligands. Further, they induced potent allogeneic T-cell responses and activated antigen-experienced T cells. These findings demonstrate that SR1 can be exploited to generate high numbers of functional pDCs and mDCs from CD34+ HPCs, providing an alternative option to Mo-DCs for immunotherapy of patients with cancer or infections.

Contains fulltext : 177224.pdf (Publisher’s version ) (Closed access) Although allogeneic stem cell transplantation (allo-SCT) can elicit graft-versus-tumor (GVT) immunity, patients often relapse due to residual tumor cells. As essential orchestrators of the immune system, vaccination with dendritic cells (DC) is an appealing strategy to boost the GVT response. Nevertheless, durable clinical responses after DC vaccination are still limited, stressing the need to improve current DC vaccines. Aiming to empower DC potency, we engineered monocyte-derived DCs to deprive them of ligands for the immune checkpoint regulated by programmed death 1 (PD-1). We also equipped them with interleukin (IL)-15 "transpresentation" skills. Transfection with short interfering (si)RNA targeting the PD-1 ligands PD-L1 and PD-L2, in combination with IL15 and IL15Ralpha mRNA, preserved their mature DC profile and rendered the DCs superior in inducing T-cell proliferation and IFNgamma and TNFalpha production. Translated into an ex vivo hematological disease setting, DCs deprived of PD-1 ligands (PD-L), equipped with IL15/IL15Ralpha expression, or most effectively, both, induced superior expansion of minor histocompatibility antigen-specific CD8+ T cells from transplanted cancer patients. These data support the combinatorial approach of in situ suppression of the PD-L inhibitory checkpoints with DC-mediated IL15 transpresentation to promote antigen-specific T-cell responses and, ultimately, contribute to GVT immunity. Cancer Immunol Res; 5(8); 710-5. (c)2017 AACR.

Autologous, patient-specific, monocyte-derived dendritic cell (MoDC) vaccines have been successfully applied in the clinical studies so far. However, the routine application of this strategy has been hampered by the difficulties in generating sufficient numbers of DC and the poor DC vaccine quality because of pathology or prior treatment received by the patients. The immunotherapeutic potential of other subsets of DC has not been thoroughly investigated because of their rarity in tissues and difficulties associated with their ex vivo generation. The high expansion and differentiation potential of CD34 hematopoietic progenitor cells (HPC), isolated from umbilical cord blood (UCB), into different DC subsets make them an attractive alternative DC source for cancer immunotherapy. Therefore, the aim of this study was to generate a large number of different DC subsets from CD34 HPC and evaluate their functionality in comparison with MoDC. Our culture protocol generated a clinically relevant number of mature CD1a myeloid DC and CD207 Langerhans cells (LC)-like DC subsets from CD34 HPC with >95% purity. Both DC subsets exhibited a cytokine profile that favors cytotoxic T-cell responses. Furthermore, UCB-DC and UCB-LC demonstrated superior induction of proliferation of both allogeneic as well as viral antigen-specific CD8 T cells, both in vitro and in vivo. Additional studies revealed that UCC-DC and UCB-LC can efficiently expand minor histocompatibility antigen (MiHA) HA-1-specific cytotoxic T cells in the peripheral blood of leukemia patients and prime MiHA HA-1-specific and HA-2-specific cytotoxic T cells in vitro. These preclinical findings support the pharmaceutical development of the described culture protocol for clinical evaluation.

The prominent role of dendritic cells (DCs) in T cell activation is the rational for DC-based immunotherapy of cancer and infectious diseases. In cancer, DC therapy aims to induce tumor-specific effector T cell responses that can reduce or eliminate the tumor, and to develop immunological memory to control tumor relapse. So far, the vast majority of DC vaccination studies have been performed with DCs differentiated from monocytes (Mo-DCs) that are loaded with tumor-associated antigens (TAAs) or minor histocompatibility antigens (MiHA). This strategy has been reported to induce the expansion of antigen-specific CD4+ and/or CD8+ T cells in the majority of patients, however only a fraction of the patients develop clinical responses. Strategies to improve the potency of DC-based vaccines are to increase the stimulatory and migratory capacity of Mo-DCs, or to use alternative DC subtypes, such as naturally circulating plasmacytoid DCs (pDCs), BDCA1+ myeloid DCs (mDCs) or BDCA3+ mDCs. These DC subsets are potent inducers of antigen-specific T cell responses, and are therefore attractive cells to exploit for DC-based therapy. However, since their frequency in blood is very low, it is a challenge to obtain high enough numbers for immunotherapy. It would be advantageous if DCs, which are phenotypically and functionally similar to blood pDCs and mDCs, could be generated from CD34+ hematopoietic progenitor cells (HPCs). Interestingly, recent findings have indicated that the aryl hydrocarbon receptor (AhR) not only regulates toxic effects of environmental contaminants, but also plays a role in modulating hematopoiesis and the immune system. For instance, it has been reported that StemRegenin 1 (SR1), a small molecule inhibitor of AhR, promotes the ex vivo expansion of human CD34+ HPCs that are able to effectively engraft immunodeficient mice. Furthermore, differentiation of Langerhans cells and monocytes in vitro from HPCs can be inhibited by the addition of the AhR agonist VAF347. In light of these data, we investigated if we could generate DC subsets from CD34+ HPCs by supplementing SR1. Therefore, we cultured CD34+ HPCs in medium containing SCF, Flt3L, IL-6, TPO supplemented with 1 μM SR1 or DMSO as control. Interestingly, addition of SR1 explicitly promoted the emergence of pDCs (CD11c-HLA-DR+CD123hiBDCA2+BDCA4+ cells), BDCA1+ mDCs (Lin1-HLA-DR+BDCA1+BDCA3- cells) and BDCA3+ mDCs (Lin1-HLA-DR+BDCA1-BDCA3+ cells). After three weeks of culture, the frequency of these DC subsets was significantly higher in cultures with SR1 compared to control conditions; 2.9% vs. 0.04% for pDCs, 4.6% vs. 0.5% for BDCA1+ mDCs and 1.1% vs. 0.1% for BDCA3+ mDCs (n=3-5 donors). The average yield after three weeks of culture with SR1 starting from 105 CD34+ UCB cells was 3.8x106 pDCs, 5.3x106 BDCA1+ mDCs and 1.2x106 BDCA3+ mDCs (n=3-5 donors). Furthermore, SR1 also promoted the differentiation of DC subsets from CD34+ cells obtained from peripheral blood of G-CSF-mobilized donors. The average frequency of DCs in these SR1-cultures was 4.7%, 3.8% and 0.9% for pDCs, BDCA1+ and BDCA3+ mDCs, respectively (n=3 donors), which is comparable to the frequency obtained from UCB CD34+ cells. But the expansion potential of G-CSF-mobilized blood CD34+ HPCs was lower than that of UCB CD34+ cells, resulting in average DC yields of 0.6x106, 0.5x106 and 0.1x106 from 105 CD34+ cells (n=3). Flow cytometry analysis demonstrated that the SR1-induced pDCs and mDCs are phenotypically comparable to their naturally occurring counterpart in blood. Furthermore, the ex vivo-generated pDCs potently responded to stimulation with TLR7 and TLR9 ligands by secreting high amounts of IFN-α and upregulating CD83, CD80, CD86 and CCR7. The HPC-mDC subsets also upregulate CD80 and CD83 upon TLR3, TLR4 or TLR7/8 ligation. Finally, both the ex vivo-generated pDCs and mDCs induced potent allogeneic T cell responses and activated CD8+ effector T cells against hematopoietic-restricted MiHA. These findings demonstrate that our SR1 culture system not only allows detailed study of DC differentiation and molecular regulations in vitro, but it also offers the opportunity to evaluate the in vivo efficacy of cultured DC subsets upon vaccination into patients with cancer and viral infections. Disclosures: Spanholtz: Glycostem Therapeutics: Employment.